package javacore.draw.gif;

import java.io.IOException;
import java.io.OutputStream;

//==============================================================================   
//  Adapted from Jef Poskanzer's Java port by way of J. M. G. Elliott.   
//  K Weiner 12/00   

class LZWEncoder
{

    private static final int EOF        = -1;

    private int              imgW, imgH;

    private byte[]           pixAry;

    private int              initCodeSize;

    private int              remaining;

    private int              curPixel;

    // GIFCOMPR.C - GIF Image compression routines
    //
    // Lempel-Ziv compression based on 'compress'. GIF modifications by
    // David Rowley (mgardi@watdcsu.waterloo.edu)

    // General DEFINEs

    static final int         BITS       = 12;

    static final int         HSIZE      = 5003;                              // 80% occupancy

    // GIF Image compression - modified 'compress'
    //
    // Based on: compress.c - File compression ala IEEE Computer, June 1984.
    //
    // By Authors: Spencer W. Thomas (decvax!harpo!utah-cs!utah-gr!thomas)
    // Jim McKie (decvax!mcvax!jim)
    // Steve Davies (decvax!vax135!petsd!peora!srd)
    // Ken Turkowski (decvax!decwrl!turtlevax!ken)
    // James A. Woods (decvax!ihnp4!ames!jaw)
    // Joe Orost (decvax!vax135!petsd!joe)

    int                      n_bits;                                         // number of bits/code

    int                      maxbits    = BITS;                              // user settable max # bits/code

    int                      maxcode;                                        // maximum code, given n_bits

    int                      maxmaxcode = 1 << BITS;                         // should NEVER generate this code

    int[]                    htab       = new int[HSIZE];

    int[]                    codetab    = new int[HSIZE];

    int                      hsize      = HSIZE;                             // for dynamic table sizing

    int                      free_ent   = 0;                                 // first unused entry

    // block compression parameters -- after all codes are used up,
    // and compression rate changes, start over.
    boolean                  clear_flg  = false;

    // Algorithm: use open addressing double hashing (no chaining) on the
    // prefix code / next character combination. We do a variant of Knuth's
    // algorithm D (vol. 3, sec. 6.4) along with G. Knott's relatively-prime
    // secondary probe. Here, the modular division first probe is gives way
    // to a faster exclusive-or manipulation. Also do block compression with
    // an adaptive reset, whereby the code table is cleared when the compression
    // ratio decreases, but after the table fills. The variable-length output
    // codes are re-sized at this point, and a special CLEAR code is generated
    // for the decompressor. Late addition: construct the table according to
    // file size for noticeable speed improvement on small files. Please direct
    // questions about this implementation to ames!jaw.

    int                      g_init_bits;

    int                      ClearCode;

    int                      EOFCode;

    // output
    //
    // Output the given code.
    // Inputs:
    // code: A n_bits-bit integer. If == -1, then EOF. This assumes
    // that n_bits =< wordsize - 1.
    // Outputs:
    // Outputs code to the file.
    // Assumptions:
    // Chars are 8 bits long.
    // Algorithm:
    // Maintain a BITS character long buffer (so that 8 codes will
    // fit in it exactly). Use the VAX insv instruction to insert each
    // code in turn. When the buffer fills up empty it and start over.

    int                      cur_accum  = 0;

    int                      cur_bits   = 0;

    int                      masks[]    = { 0x0000, 0x0001, 0x0003, 0x0007, 0x000F, 0x001F, 0x003F, 0x007F, 0x00FF,
            0x01FF, 0x03FF, 0x07FF, 0x0FFF, 0x1FFF, 0x3FFF, 0x7FFF, 0xFFFF };

    // Number of characters so far in this 'packet'
    int                      a_count;

    // Define the storage for the packet accumulator
    byte[]                   accum      = new byte[256];

    // ----------------------------------------------------------------------------
    LZWEncoder(int width, int height, byte[] pixels, int color_depth)
    {
        this.imgW = width;
        this.imgH = height;
        this.pixAry = pixels;
        this.initCodeSize = Math.max(2, color_depth);
    }

    // Add a character to the end of the current packet, and if it is 254
    // characters, flush the packet to disk.
    void char_out(byte c, OutputStream outs) throws IOException
    {
        this.accum[this.a_count++] = c;
        if (this.a_count >= 254)
        {
            this.flush_char(outs);
        }
    }

    // Clear out the hash table

    // table clear for block compress
    void cl_block(OutputStream outs) throws IOException
    {
        this.cl_hash(this.hsize);
        this.free_ent = this.ClearCode + 2;
        this.clear_flg = true;

        this.output(this.ClearCode, outs);
    }

    // reset code table
    void cl_hash(int hsize)
    {
        for (int i = 0; i < hsize; ++i)
        {
            this.htab[i] = -1;
        }
    }

    void compress(int init_bits, OutputStream outs) throws IOException
    {
        int fcode;
        int i /* = 0 */;
        int c;
        int ent;
        int disp;
        int hsize_reg;
        int hshift;

        // Set up the globals: g_init_bits - initial number of bits
        this.g_init_bits = init_bits;

        // Set up the necessary values
        this.clear_flg = false;
        this.n_bits = this.g_init_bits;
        this.maxcode = this.MAXCODE(this.n_bits);

        this.ClearCode = 1 << (init_bits - 1);
        this.EOFCode = this.ClearCode + 1;
        this.free_ent = this.ClearCode + 2;

        this.a_count = 0; // clear packet

        ent = this.nextPixel();

        hshift = 0;
        for (fcode = this.hsize; fcode < 65536; fcode *= 2)
        {
            ++hshift;
        }
        hshift = 8 - hshift; // set hash code range bound

        hsize_reg = this.hsize;
        this.cl_hash(hsize_reg); // clear hash table

        this.output(this.ClearCode, outs);

        outer_loop:
        while ((c = this.nextPixel()) != EOF)
        {
            fcode = (c << this.maxbits) + ent;
            i = (c << hshift) ^ ent; // xor hashing

            if (this.htab[i] == fcode)
            {
                ent = this.codetab[i];
                continue;
            }
            else
                if (this.htab[i] >= 0) // non-empty slot
                {
                    disp = hsize_reg - i; // secondary hash (after G. Knott)
                    if (i == 0)
                    {
                        disp = 1;
                    }
                    do
                    {
                        if ((i -= disp) < 0)
                        {
                            i += hsize_reg;
                        }

                        if (this.htab[i] == fcode)
                        {
                            ent = this.codetab[i];
                            continue outer_loop;
                        }
                    }
                    while (this.htab[i] >= 0);
                }
            this.output(ent, outs);
            ent = c;
            if (this.free_ent < this.maxmaxcode)
            {
                this.codetab[i] = this.free_ent++; // code -> hashtable
                this.htab[i] = fcode;
            }
            else
            {
                this.cl_block(outs);
            }
        }
        // Put out the final code.
        this.output(ent, outs);
        this.output(this.EOFCode, outs);
    }

    // ----------------------------------------------------------------------------
    void encode(OutputStream os) throws IOException
    {
        os.write(this.initCodeSize); // write "initial code size" byte

        this.remaining = this.imgW * this.imgH; // reset navigation variables
        this.curPixel = 0;

        this.compress(this.initCodeSize + 1, os); // compress and write the pixel data

        os.write(0); // write block terminator
    }

    // Flush the packet to disk, and reset the accumulator
    void flush_char(OutputStream outs) throws IOException
    {
        if (this.a_count > 0)
        {
            outs.write(this.a_count);
            outs.write(this.accum, 0, this.a_count);
            this.a_count = 0;
        }
    }

    final int MAXCODE(int n_bits)
    {
        return (1 << n_bits) - 1;
    }

    // ----------------------------------------------------------------------------
    // Return the next pixel from the image
    // ----------------------------------------------------------------------------
    private int nextPixel()
    {
        if (this.remaining == 0)
        {
            return EOF;
        }

        --this.remaining;

        byte pix = this.pixAry[this.curPixel++];

        return pix & 0xff;
    }

    void output(int code, OutputStream outs) throws IOException
    {
        this.cur_accum &= this.masks[this.cur_bits];

        if (this.cur_bits > 0)
        {
            this.cur_accum |= (code << this.cur_bits);
        }
        else
        {
            this.cur_accum = code;
        }

        this.cur_bits += this.n_bits;

        while (this.cur_bits >= 8)
        {
            this.char_out((byte) (this.cur_accum & 0xff), outs);
            this.cur_accum >>= 8;
            this.cur_bits -= 8;
        }

        // If the next entry is going to be too big for the code size,
        // then increase it, if possible.
        if (this.free_ent > this.maxcode || this.clear_flg)
        {
            if (this.clear_flg)
            {
                this.maxcode = this.MAXCODE(this.n_bits = this.g_init_bits);
                this.clear_flg = false;
            }
            else
            {
                ++this.n_bits;
                if (this.n_bits == this.maxbits)
                {
                    this.maxcode = this.maxmaxcode;
                }
                else
                {
                    this.maxcode = this.MAXCODE(this.n_bits);
                }
            }
        }

        if (code == this.EOFCode)
        {
            // At EOF, write the rest of the buffer.
            while (this.cur_bits > 0)
            {
                this.char_out((byte) (this.cur_accum & 0xff), outs);
                this.cur_accum >>= 8;
                this.cur_bits -= 8;
            }

            this.flush_char(outs);
        }
    }
}